No news here. They make money selling at employee discount for the reasons you stated. But the service dept. is where the real money is.I've paid less than invoice on the last 7 cars I have bought. At invoice they are making money. Whether it relates to net profit depends on how well they manage their dealership.
Edit: If the margin on a new vehicle was 5.8% they wouldn't be in the business of selling cars. There are extra margins, holdbacks, volume discounts and rebates to the dealer that also come into play.